Issues in Runtime Statistics

[kunwp1]

There are three main issues with runtime statistics:

1. Cumulative Statistics: Currently, runtime statistics are recorded every 0.5 seconds, storing only the difference (diff) values for tuple counts and processing times. However, @Xiao-zhen-Liu has requested that we store cumulative values instead.
2. Timestamp Accuracy: The timestamp recorded in runtime statistics reflects the time when the record is inserted into the table, rather than when the statistics were actually measured. It should instead capture the precise time of measurement.
3. Missing Tuple Size: Currently, runtime statistics only store the tuple count. To provide more comprehensive insights, the tuple size should also be included.